An auto-feed device for feeding media to blasting machine

ABSTRACT

A device for continuously feeding media from an unpressurised container to a pressurised chamber without depressurising the chamber is described. The device comprises a cylinder having two chambers defined by a top wall, and bottom wall, and a dividing wall intermediate the top and the base walls. The top wall comprises an inlet aperture for inlet of media and a pressure equalisation aperture. The dividing wall comprises an inlet aperture for receipt of media from the first chamber and a pressure equalisation aperture in fluid communication with a first pressure equalisation conduit that extends from the second aperture to a top of the first chamber. The bottom wall comprises an inlet aperture for supply of media to the blasting machine and a pressure equalisation aperture in fluid communication with a second pressure equalisation conduit that extends from the pressure equalisation aperture to a top of the second chamber. Closure means associated with the inlet and pressure equalisation apertures in the top, dividing and bottom walls, are provided, each closure means being adapted to open and close the apertures in sequence in which the pressure equalisation aperture is opened prior to the inlet aperture aperture.

BACKGROUND TO THE INVENTION

The invention relates to device for feeding media to a blasting machine of the type that projects a particulate media at a surface for the purpose of cleaning the surface.

Blasting machines of the above-referenced type are known and generally comprise a tank/reservoir for the media, an air/media mixing chamber where the media is mixed with compressed air and accelerated into a delivery line, and a nozzle in fluid communication with the mixing chamber for directing the media/air mixture at a surface to be treated. A machine of the above-referenced type is described in Applicants International Patent Application No: PCT/EP2007/002421. In order for this machine to operate correctly, and particularly to enable consistent and smooth delivery of media from the reservoir/tank to the mixing chamber, it is necessary to equalise the pressure between the tank and the mixing chamber. In PCT/EP2007/002421, this is achieved by employing a pressure equalisation conduit that provides fluid communication between the pressurised mixing chamber and the interior of the media tank, which results in the tank being pressurised. A problem with this arrangement is that when the tank needs to be re-filled with media, the machine needs to be switched off, as otherwise the opening the tank will release the pressure in the tank and consequently release the pressure in the mixing chamber due to the pressure equalisation conduit.

It is an object of the invention to overcome this problem.

STATEMENTS OF INVENTION

The Applicant has addressed the above-referenced problem by providing an auto-feed device having a two chambers, a first chamber for receiving media from outside (i.e. from a hopper), and a second chamber for receiving media from the first chamber and delivering the media to a pressurised environment, for example a tank/reservoir of a blasting machine. The device includes pressure equalisation means for equalising the pressure between the tank and the second chamber, and between the second chamber and the first chamber. Thus, when the first chamber receives media from an external source, the first chamber will be at ambient pressure and the second chamber will be pressurised. Prior to delivering the media to the second chamber, the pressure equalisation means will equalise pressure between the first and second chambers, so that both chambers are at ambient pressure. Thus, delivery between the two chambers will not be inhibited by pressure differences between the chambers. Upon receipt of media, the pressure equalisation means will equalise pressure between the second chamber and the pressurised media tank, resulting in the second chamber being pressurised. Once pressurised, the media will be delivered from the second chamber to the media tank/reservoir. The pressure equalisation means comprise pressure equalisation conduits that are located within the chambers, and provide fluid communication from an aperture in the base of the chamber to a point at or close to the top of the chamber. This means that the pressure equalisation means can be located within the device, and avoids the use of external tubes connecting the chambers. The fact that the outlet of the pressure equalisation conduit is located at the top of the chamber means that the media is not disturbed during pressure equalisation step, thus ensuring a steady and undisturbed flow of media from one chamber to the next.

Accordingly, in the first aspect, the invention broadly provides a device for conveying material/media from a first environment having a first pressure to a second environment having a second pressure without substantially altering the pressure in the second environment and/or the first environment, for example continuously feeding media from an unpressurised container (for example a hopper) to a pressurised chamber (for example a pressurised tank of a blasting machine) without depressurising the chamber, the device comprising:

-   -   a cylinder having two chambers defined by a top wall, and bottom         wall, and a dividing wall intermediate the top and the base         walls,     -   the top wall comprising an inlet aperture for inlet of media and         a pressure equalisation aperture,     -   the dividing wall comprising an inlet aperture for receipt of         media from the first chamber and a pressure equalisation         aperture in fluid communication with a first pressure         equalisation conduit that extends from the second aperture to a         top of the first chamber,     -   the bottom wall comprising an inlet aperture for supply of media         to the blasting machine and a pressure equalisation aperture in         fluid communication with a second pressure equalisation conduit         that extends from the pressure equalisation aperture to a top of         the second chamber,     -   a first closure means associated with the inlet aperture in the         top wall;     -   a second closure means for the inlet and pressure equalisation         apertures in the dividing wall and adapted to open and close the         apertures in sequence in which the pressure equalisation         aperture is opened prior to the inlet aperture, and     -   a third closure means for the inlet and pressure equalisation         apertures in the bottom wall and adapted to open and close the         apertures in sequence in which the pressure equalisation         aperture is opened prior to the inlet aperture aperture.

Typically, the device comprises actuation means for the first second and third closure means, the actuation means configured to actuate the closure means so that the first and third closure means are actuated to close apertures in the top and bottom walls simultaneously with the second closure means being actuated to open the apertures in the dividing wall. The actuation means may comprise a pair of cams mounted on a drive shaft for rotation therewith about an axis of the shaft, wherein a first cam is operatively connected to the first and third closure means and the second cam is operatively connected to the second closure means. Suitably, the actuation means comprises a motor for rotating the drive shaft. The actuation means is generally disposed above the upper chamber.

Preferably, one or both of the closure means comprises an actuation rod that is located within a pressure equalisation conduit. Thus, the closure means may be operated using rods that are disposed within the device, thereby obviating the need for external tubes and holes in the sidewalls of the device which would be prone to corrosion and leakage. Further, the pressure equalisation conduit provides means for equalisation pressure between chambers and also protects the actuation rod from the media.

Typically, the closure means comprises a closure disposed on the end of an actuation rod, in which the closure and actuation rod are disposed within the device such that raising of the actuation rod brings the closure into engagement with an aperture from beneath the aperture. This provides a particularly effective means of closing the apertures in the presence of high operating pressures.

The closure means for the inlet and pressure equalisation apertures in the dividing wall suitably comprises two closures operatively connected to a first actuation rod, wherein the first actuation rod is mounted within the first pressure equalisation conduit.

Typically, the first actuation rod extends through the top wall, the first pressure equalisation conduit and the pressure equalisation aperture in the dividing wall and projects into the second chamber, and in which the two closures are operatively connected to the first actuation rod beneath the dividing wall.

The closure means for the inlet and pressure equalisation apertures in the bottom wall comprises two closures operatively connected to a second actuation rod, wherein the second actuation rod is mounted within the second pressure equalisation conduit.

Typically, the second actuation rod extends through the top wall, the dividing wall, the second pressure equalisation conduit and the pressure equalisation aperture in the bottom wall and projects into the second chamber, and in which the two closures are operatively connected to the second actuation rod beneath the bottom wall.

Preferably, the or each closure comprises a conical member, ideally a frustoconical member, that engages an aperture from beneath.

In one embodiment, the actuation rod, ideally a base of the actuation rod, comprises a lateral arm, wherein a first of the closures is mounted to the bottom of the rod and a second of the closures is mounted on the lateral arm in a spaced-apart relationship to the first closure. Typically, the first closure is configured to close the pressure equalisation aperture, and the second closure is configured to close the media inlet aperture.

Typically, the second closure is mounted to the lateral arm by means of a resiliently deformable fixture, for example a helical spring. Ideally, the second closure is disposed with respect to the first closure such that upon raising the actuation rod the second closure engages its corresponding aperture prior to the first closure engaging its corresponding aperture. In this manner, when the actuation rod is raised, the second closure will close the media inlet aperture while the pressure equalisation aperture is still open. Likewise, when the actuation rod is lowered, the pressure equalisation aperture will open prior to the opening of the media inlet aperture. This allows the opening and closing of the apertures to be carried out in a sequential manner, allowing pressure to be equalised between chamber prior to opening of the media inlet aperture and transfer of media between chambers.

In one embodiment, the first pressure equalisation conduit extends the length of the first chamber and comprises an aperture at or adjacent a top of the conduit.

In one embodiment, the second pressure equalisation conduit extends the length of the first and second chambers and comprises an aperture at or adjacent a top of the second chamber.

Suitably, the device comprises an inlet chamber above the first chamber for directing media from an unpressurised media container, for example a hopper, to the inlet aperture of the top wall. Preferably, a top of the inlet chamber comprises means for operatively connecting to an outlet of the unpressurised media container.

Typically, the device comprises a delivery chamber disposed beneath the second chamber for receiving media from the second chamber and directing the received media to the pressurised chamber.

Suitably, the first environment is at ambient pressure, for example an unsealed container or hopper.

Typically, the second environment is pressurised, for example a pressurised chamber such as a pressurised tank or mixing chamber of a blasting machine.

Preferably, the pressurised chamber is a pressurised tank of a blasting machine. Thus, the device of the invention may be employed to continuously feed media into a pressurised tank of a blasting machine without depressurisation of the pressurised tank. This enables the blasting machine to be continuously used for long periods of time without having to turn off the machine to re-fill the media tank.

In another embodiment, the pressurised chamber is a mixing chamber of a blasting machine. In this embodiment, the device of the invention is used as a dosing device of a blasting machine, in which the device continuously doses media from an unpressurised tank to a mixing chamber of a blasting machine.

In another aspect, the invention provides a blasting machine of the type having a pressurised tank for media, the machine comprising:

a pressurised tank for media;

a mixing chamber for mixing media with compressed air;

a dosing device adapted to receive media from the pressurised tank and dose the media into the mixing chamber;

a nozzle adapted to receive the mixture of media and compressed air from the mixing chamber and direct the mixture at a surface to be treated; and

a device according to the invention for continuously feeding media from an unpressurised container to the pressurised tank.

In another embodiment, the invention provides a blasting machine comprising:

a tank for media;

a mixing chamber for mixing media with compressed air;

a dosing device adapted to receive media from the tank and dose the media into a supply of compressed air; and

a nozzle adapted to receive the mixture of media and compressed air and direct the mixture at a surface to be treated;

wherein the dosing device comprises a device according to the invention configured to continuously feeding media from the tank into the supply of compressed air.

In another aspect, the invention provides a method for continuously feeding media from a first environment having a first pressure to a second environment having a second pressure, for example from an unpressurised media container to a pressurised chamber, which method employs a device of the invention, the method comprising the steps of:

-   -   actuating the closure in the top wall to open the aperture and         allow a dose of media fall into the first chamber, wherein the         inlet and pressure equalisation apertures in the dividing wall         are both closed by the closure means and in which the pressure         in the first chamber is ambient pressure;     -   actuating the closure in the top wall to close the aperture;     -   actuating the closure means for the inlet and pressure         equalisation apertures in the dividing wall to open the         apertures in sequence with the pressure equalisation aperture         being opened prior to the media inlet aperture, whereby the         pressure in the second chamber is equalised with the pressure in         the first chamber just prior to the dose of media in the first         chamber falling into the second chamber;     -   actuating the closure means for the inlet and pressure         equalisation apertures in the dividing wall to close the         apertures; and     -   actuating the closure means for the inlet and pressure         equalisation apertures in the bottom wall to open the apertures         in sequence with the pressure equalisation aperture being opened         prior to the media inlet aperture, whereby the pressure in the         second chamber is equalised with the pressure in the pressurised         chamber just prior to the dose of media in the second chamber         falling into the pressurised chamber.

In this specification, the term “unpressurised” means ambient pressure. In this specification, the term “pressurised” means a pressure significantly greater than ambient, for example 0.1 to 20.0 Bar, more typically 0.5 to 10 Bar.

Although the embodiments of the invention described herein primarily relate to a device for continuously feeding media from an unpressurised environment to a pressurised environment, it will be appreciated that it could likewise function in feeding media from a pressurised environment to an unpressurised environment, or between high pressure environments having different pressures or low pressure environments having different pressures.

In this specification, the term “media” is primarily intended to mean media that is employed for blasting a surface, for example sand or calcium carbonate, however the term also encompasses other flowable materials, for example powders, flakes, pellets, particulates, granulates and the like.

The invention also relates to a device for continuously feeding media from a first environment having a first pressure to a second environment having a second pressure without substantially altering the pressure in the second environment, the device comprising:

-   -   a cylinder having an intermediate chamber defined between a top         wall and a dividing wall, a lower chamber defined by the         dividing wall and a bottom wall, and a top chamber disposed         above the intermediate chamber     -   the top wall comprising an inlet aperture for inlet of media and         a pressure equalisation aperture,     -   the dividing wall comprising an inlet aperture for receipt of         media from the first chamber and a pressure equalisation         aperture,     -   the bottom wall comprising an inlet aperture for supply of media         to the blasting machine and a pressure equalisation aperture,     -   a first closure means associated with the inlet aperture in the         top wall and comprising a first actuation rod that extends from         the top chamber through the pressure equalisation aperture and a         closure operatively connected to a bottom of the first actuation         rod for closing the inlet aperture,     -   a first conduit extending from the pressure equalisation         aperture in the dividing wall through a conduit aperture in the         top wall,     -   a second closure means associated with the inlet and pressure         equalisation apertures in the dividing wall and comprising a         second actuation rod that is mounted within the first conduit         and closure means operatively connected to a bottom of the         second actuation rod for closing the inlet and pressure         equalisation apertures in the dividing walls,     -   a second conduit extending from the pressure equalisation         aperture in the bottom wall through conduit apertures in the         dividing and top walls, and     -   a third closure means associated with the inlet and pressure         equalisation apertures in the bottom wall and comprising a third         actuation rod that is mounted within the second conduit and         closure means operatively connected to a bottom of the third         actuation rod for closing the inlet and pressure equalisation         apertures in the top walls.

Typically, the top chamber comprises a central chamber for receiving media and feeding media to the inlet aperture in the top wall, and a peripheral chamber, wherein the tops of the actuation rods are disposed within the peripheral chamber.

Suitably, the device includes actuation means for the closure means disposed within the peripheral chamber of the top chamber.

Typically, the actuation means comprises two cams mounted to a drive shaft, in which the first cam is operatively connected to the first and third closure means and the second cam is operatively connected to the second closure means.

BRIEF DESCRIPTION OF THE FIGURES

The invention will be more clearly understood from the following description of some embodiments thereof, with reference to the accompanying drawings, in which:

FIG. 1 a sectional elevational view of an auto-feed device according to the invention, shown with both chambers empty;

FIG. 2 is a detailed view of the auto-feed device of FIG. 1 showing the inlet aperture in the top and bottom wall closed, and the inlet aperture in the dividing wall open;

FIG. 3 a sectional elevational view of an auto-feed device of FIG. 1, shown with the first chamber charged with a dose of media; and the inlet aperture in the dividing wall closed and the pressure equalisation conduit in the dividing wall open to allow pressure equalisation between the first and second chambers;

FIG. 4 is a detailed view of the auto-feed device of FIG. 3;

FIG. 5 is detailed view of the auto-feed device of FIG. 3 shown from a different angle, and showing the aperture in the dividing wall open and the apertures in the top and bottom walls closed;

FIG. 6 a sectional elevational view of the auto-feed device of FIG. 1, shown with the first chamber empty and the second chamber charged with media, the inlet aperture in the dividing wall open, the inlet aperture in the bottom wall closed, and the pressure equalisation aperture in the bottom wall open;

FIG. 7 is a detailed view of the auto-feed device of FIG. 6, showing the dose of media in the second chamber and a dose of media in the inlet chamber above the first chamber;

FIG. 8 is a detailed view of the auto-feed device of FIG. 6, showing the apertures in the dividing wall closed and pressure equalisation aperture in the bottom wall open to equalise pressure between the second chamber and outlet and inlet aperture in the bottom wall to allow the dose of media fall into the outlet;

FIG. 9 is a sectional elevational view of the auto-feed device of FIG. 1, showing the inlet aperture in the top wall open and a dose of media in the first chamber, and the inlet aperture in the bottom wall open and a dose of media in the outlet;

FIG. 10 is an illustration of a blasting system comprising a blasting machine, a hopper for media and a device according to the invention; and

FIG. 11 is an illustration of a blasting machine which employs a device according to the invention as a dosing device.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the drawings, and initially to FIGS. 1 and 2, there is illustrated a device for continuously feeding media from an unpressurised container to a pressurised chamber, indicated generally by the reference numeral 1. In this case, the device is an auto-feed device for feeding media from a hopper (not shown) to a pressurised tank of a blasting machine (not shown) of the type described in PCT/EP2007/002421. The device 1 comprises a generally cylindrical body 2 having a top wall 3, a bottom wall 4 and a dividing wall 5, in which the top wall 3 and dividing wall 5 define a first chamber 6 and the dividing wall 5 and bottom wall 4 define a second chamber 7. An inlet chamber 8 is provided above the first chamber, and is adapted to engage an outlet of the hopper. An outlet chamber 9 is provided below the second chamber, and in use is adapted to sealingly engage with an inlet of the pressurised tank of the blasting machine.

Referring particularly to FIG. 2, the top wall 3 includes a media inlet aperture 10 and a pressure equalisation aperture 11 that remains open, and a closure means that can be actuated to open and close the aperture 10, the closure means comprising an actuation rod 12 that projects through the pressure equalisation aperture 11 in the top wall 3, a transverse arm 14 and a conical closure member 15 mounted to the transverse arm by means of a helical spring 16.

Referring particularly to FIGS. 1 and 7, the dividing wall 5 includes a media inlet aperture 20 and a pressure equalisation aperture 21, and a closure means that can be actuated to open and close the apertures 20 and 21 in sequence, the closure means comprising an actuation rod 22, a first conical closure member 23 mounted to the base of the rod 22, a transverse arm 24 and a second conical closure member 25 mounted to the transverse arm by means of a helical spring 26. A pressure equalisation conduit 27 is provided for providing fluid communication from the second chamber 7 to a top of the first chamber 6 via an aperture 28 in the conduit 27. The pressure equalisation conduit 27 extends through the top wall 3, and the actuation rod 22 is mounted in the pressure equalisation conduit. A seal (not shown) is mounted in a top of the pressure equalisation conduit allow movement of the actuation rod without a change of pressure in the conduit.

Referring particularly to FIGS. 1 and 2, the bottom wall 4 includes a media inlet aperture 30 and a pressure equalisation aperture 31, and a closure means that can be actuated to open and close the apertures 30 and 31 in sequence, the closure means comprising an actuation rod 32, a first conical closure member 33 mounted to the base of the rod 32, a transverse arm 34 and a second conical closure member 35 mounted to the transverse arm by means of a helical spring 36. A pressure equalisation conduit 37 is provided for providing fluid communication from the third chamber 9 to a top of the second chamber 7 via an aperture 38 in the conduit 37. The pressure equalisation conduit 37 extends through the dividing wall 5 and the top wall 3, and the actuation rod 32 is mounted in the pressure equalisation conduit. A seal (not shown) is mounted in a top of the pressure equalisation conduit allow movement of the actuation rod without a change of pressure in the conduit.

In practice, the top, dividing and bottom walls will have a generally concave shape to ensure that media falls towards the respective inlet apertures.

An important aspect of the present invention is the equalisation of pressure between chambers prior to transfer of media from one chamber to another. Without pressure equalisation, the transfer of media is not possible. The inlet chamber located above the first chamber will generally always be at ambient pressure, and the outlet chamber located below the second chamber (which in the above embodiment is in fluid communication with the pressurised media tank) will always be pressurised (i.e. a pressure of X to Y). Thus, when the first chamber contains a dose of media, it will be at ambient pressure and the second chamber will be pressurised. In order to transfer media from the first chamber to the second chamber, the pressure equalisation aperture 21 in the dividing wall 5 needs to be opened while the media inlet aperture 20 is still closed (as in FIGS. 3 and 4) to allow equalisation of pressure between the two chambers. The pressure equalisation conduit 27 ensures that the media in the first chamber is not unduly disturbed during pressure equalisation, by the provision of the aperture 28 in the conduit 27 in an upper part of the chamber, above the level of the media. Once pressure is equalised (which in practice will occur almost instantaneously), the inlet aperture is opened to allow media fall into the second chamber 7.

Thus, the closure means for the apertures in the top, bottom and dividing walls need to ensure that the apertures open and close in sequence, with the pressure equalisation aperture opening first and the media inlet aperture opening afterwards, in practice immediately afterwards. This achieved by employing an actuating rod with two closures operatively connected to the rod, a first closure for the pressure equalisation aperture which is fixed to the rod for movement therewith, and a second closure for the inlet aperture which is fixed to the rod by means of a lateral arm, and is fixed to the arm by means of a resiliently deformable member that is biased into an extended position, for example a spring such as a helical spring, which allows a relative movement between the rod and the closure. Thus, when both closures are engaged with their respective apertures, downward movement of the rod will move the first closure out of engagement with the pressure equalisation aperture, whereas the second closure will remain in engagement with the inlet aperture due to the biasing effect of the spring until the spring is fully extended at which point further downward movement will open the inlet aperture. In this manner, a temporal and sequential opening of the apertures is achieved.

The device also includes control means for controlling the closure means associated with the top, dividing and bottom walls. Various control means may be employed, including a cam mechanism or motors controlled by a processor, the details and construction would be known to a person skilled in the art and which will not be described in more detail herein. The sequence of opening and closing of the closures means associated with the three walls is generally as follows:

Stage 1: at a start of the process, the closures associated with the top and bottom walls will be closed and the closures associated with the dividing wall will be open. In this configuration, the first and second chambers will be unpressurised. Media is located in the inlet chamber above the first chamber (FIGS. 1 and 2).

Stage 2: the closures associated with the dividing wall will be closed first, and the closures associated with the top and bottom walls will then be opened. In this configuration, the first chamber will be unpressurised, and the second chamber pressurised. Media will fall into the first chamber (FIGS. 3 and 4).

Stage 3: the closures associated with the top and bottom walls will be closed first, and the closures associated with the dividing wall will be opened second. In this configuration, the first and second chambers will be unpressurised and the media will fall into the second chamber (FIGS. 5, 6 and 7).

Stage 4: the closures associated with the dividing wall will be closed first, and the closures associated with the top and bottom walls will be opened second. The second chamber will be pressurised prior to the dose of media falling into the outlet chamber. Simultaneously, a dose of media will fall from the inlet chamber into the first chamber, both of which will be unpressurised (FIGS. 8 and 9).

Repeating these steps in sequence will enable a continuous feeding of media from the unpressurised container (i.e. hopper) to the pressurised tank of the blasting machine without compromising the operating pressure in the tank.

Referring to FIG. 10, there is illustrated a blasting system according to the invention and indicated generally by the reference numeral 50, and comprising a blasting machine having a pressurised media tank 51, dosing device and mixing chamber 52, pressurised fluid line 53 feeding pressurised air into the mixing chamber 52, pressurised media supply line 54 leading to a nozzle 55. A pressure equalisation conduit (not shown) is provided between the tank 52 and the mixing chamber 52. A hopper 56 is provided for containing media, the hopper having an outlet 57 that feeds media into an auto-feeding device of the invention 58. In use, media is continuously fed into the auto-feed device 58 from the hopper 56, and the auto-feed device feeds doses of media into the pressurised media tank 51 without any substantial pressure drop in the tank, then enabling the blasting machine to continue operating while the tank is being filled.

Referring to FIG. 11, an alternative embodiment of the invention is described in which parts similar to that described with reference to the previous embodiment are assigned the same reference numerals. In this embodiment, the auto-feed device of the invention is employed as a dosing device for the blasting machine, to feed media from an unpressurised hopper 56 into a mixing chamber 59. In use, the device of the invention acts as a dosing and metering device for dosing media from the hopper 56 into the pressurised mixing chamber 59 of the blasting machine. The rate of dosing of the media may be controlled by altering the timing of the opening and closing of the apertures to speed up or slow down the dosing rate as is required.

The invention is not limited to the embodiments hereinbefore described which may be varied in construction and detail without departing from the spirit of the invention. 

1. A device (1) for continuously feeding media from a first environment having a first pressure to a second environment having a second pressure without substantially altering the pressure in the second environment, the device comprising: a cylinder having two chambers defined by a top wall (3), and bottom wall (4), and a dividing wall (5) intermediate the top and the base walls, the top wall (3) comprising an inlet aperture (10) for inlet of media and a pressure equalisation aperture, the dividing wall (5) comprising an inlet aperture (20) for receipt of media from the first chamber and a pressure equalisation aperture (21) in fluid communication with a first pressure equalisation conduit (27) that extends from the second aperture to a top of the first chamber (6), the bottom wall comprising an inlet aperture (30) for supply of media to the blasting machine and a pressure equalisation aperture (31) in fluid communication with a second pressure equalisation conduit (37) that extends from the pressure equalisation aperture to a top of the second chamber (7), a first closure means associated with the inlet aperture (10) in the top wall (3); a second closure means for the inlet and pressure equalisation apertures (20, 21) in the dividing wall (5) and adapted to open and close the apertures in sequence in which the pressure equalisation aperture is opened prior to the inlet aperture, and a third closure means for the inlet and pressure equalisation apertures (30, 31) in the bottom wall (4) and adapted to open and close the apertures in sequence in which the pressure equalisation aperture is opened prior to the inlet aperture aperture.
 2. A device as claimed in claim 1 including actuation means for the first second and third closure means, the actuation means configured to actuate the closure means so that the first and third closure means are actuated to close apertures in the top and bottom walls simultaneously with the second closure means being actuated to open the apertures in the dividing wall.
 3. A device as claimed in claim 1 in which one or both of the closure means comprises an actuation rod (32, 22) that is located at along a part of its length within a pressure equalisation conduit (37, 27).
 4. A device as claimed in claim 3 in which the closure means comprises a closure disposed on the end of an actuation rod, in which the closure and actuation rod are disposed within the device such that raising of the actuation rod brings the closure into engagement with an aperture from beneath the aperture.
 5. A device as claimed in claim 4 in which the closure means for the inlet and pressure equalisation apertures in the dividing wall comprises two closures (23, 25) operatively connected to a first actuation rod (22), wherein the first actuation rod is mounted within the first pressure equalisation conduit, in which the first actuation rod (22) optionally extends through the top wall (3), and the pressure equalisation aperture (21) in the dividing wall (5) and projects into the second chamber, and in which the two closures (23, 25) are optionally operatively connected to the first actuation rod beneath the dividing wall.
 6. A device as claimed in claim 4 in which the closure means for the inlet and pressure equalisation apertures in the bottom wall comprises two closures (33, 35) operatively connected to a second actuation rod (32), wherein the second actuation rod is mounted within the second pressure equalisation conduit, in which the second actuation rod (32) optionally extends through the top wall, the dividing wall, and the pressure equalisation aperture (31) in the bottom wall (4) and projects into the second chamber, and in which the two closures (33, 35) are optionally operatively connected to the second actuation rod beneath the bottom wall.
 7. A device as claimed in claim 4 in which the closures (23, 25, 33, 35) comprise conical members that engage the apertures from beneath.
 8. A device as claimed in claim 1 and including an inlet chamber (8) above the first chamber (6) for directing media from the first environment to the inlet aperture of the top wall.
 9. A device as claimed in claim 1 including a delivery chamber (9) disposed beneath the second chamber (7) for receiving media from the second chamber and directing the received media to the second environment.
 10. A device as claimed in claim 1 in which the second environment is a pressurised tank of a blasting machine or a mixing chamber of a blasting machine or a mixing chamber of a blasting machine.
 11. A blasting machine (1) of the type having a pressurised tank for media, the machine comprising: a pressurised tank for media (51); a dosing device (52) adapted to receive media from the pressurised tank and dose the media into a supply of compressed air (53); a nozzle (55) adapted to receive the mixture of media and compressed air and direct the mixture at a surface to be treated; and a device (1) according to any of claims 1 to 11 in which the first environment is an unpressurised container or hopper and the second environment is the pressurised tank.
 12. A blasting machine (50) comprising: a tank (51) for media; a mixing chamber (59) for mixing media with compressed fluid; a dosing device (58) adapted to receive media from the tank and dose the media into the mixing chamber; a nozzle (55) adapted to receive the mixture of media and compressed fluid and direct the mixture at a surface to be treated; wherein the dosing device (58) comprises a device according to any of claims 1 to 11 in which the first environment is the tank for media and the second environment is the mixing chamber.
 13. A method for continuously feeding media from a first environment having a first pressure to a second environment having a second pressure without substantially altering the pressure in the second environment, which method employs a device of claim 1, the method comprising the steps of: actuating the closure in the top wall to open the aperture and allow a dose of media fall from the first environment into the first chamber, wherein the inlet and pressure equalisation apertures in the dividing wall are both closed by the closure means and in which the pressure in the first chamber is ambient pressure; actuating the closure in the top wall to close the aperture; actuating the closure means for the inlet and pressure equalisation apertures in the dividing wall to open the apertures in sequence with the pressure equalisation aperture being opened prior to the media inlet aperture, whereby the pressure in the second chamber is equalised with the pressure in the first chamber just prior to the dose of media in the first chamber falling into the second chamber; actuating the closure means for the inlet and pressure equalisation apertures in the dividing wall to close the apertures; and actuating the closure means for the inlet and pressure equalisation apertures in the bottom wall to open the apertures in sequence with the pressure equalisation aperture being opened prior to the media inlet aperture, whereby the pressure in the second chamber is equalised with the pressure in the pressurised chamber just prior to the dose of media in the second chamber falling into the second environment. 